1. Field of the Invention
The present invention relates to an apparatus adapted to detect disturbances or noises which influence a tired wheel (hereinafter referred to as "vehicle wheel" or "wheel") of a motor vehicle, and a method of using such disturbance detecting apparatus.
2. Discussion of the Related Art
For controlling a motor vehicle, it is useful and significant to know the behaviors and changing characteristics of the wheels of the vehicle, because the wheels are the only components at which the vehicle contacts a road surface. However, it is not easy to directly detect the behaviors and the changing characteristics of the vehicle wheels during running of the vehicle, since the wheels are attached to the body of the vehicle through a suspension system such that the wheels are displaceable relative to the vehicle body, and since the wheels are rotated.
For a motor vehicle equipped with wheels having tires that are inflated by compressed air so as to maintain a suitable degree of elasticity, for example, the air pressure in the tires has an important effect or influence on the operating characteristics of the wheels. Accordingly, it is desirable to detect the air pressure levels of the wheel tires, but the detection of the tire pressure is also difficult.
The air pressure of a wheel tire may be detected by a pneumatic pressure sensor attached thereto. However, it is not easy to transmit the output of the sensor on the rotating tire to a desired position on the vehicle body while the vehicle is running. It is also possible to determine the tire pressure on the basis of a change in the distance between the road surface and the vehicle body, which change occurs due to deformation of the wheel tire as the tire pressure is lowered. Further, it is possible to estimate a decrease of the tire pressure of one or more wheels as compared with the tire pressure of the other wheels, depending upon the detected rotating speeds of the wheels, based on a fact that the tire pressure decreases with an increase in the rotating speed. However, these methods do not assure accurate detection of the tire pressure. In particular, the latter method does not permit the detection of a decrease of the tire pressure of any wheel if the tire pressure levels of all the wheels whose speeds are detected are lowered.
In the light of the difficulty in detecting a change in the tire pressure of a vehicle wheel, JP-A-62-149502 proposes a tire pressure detecting apparatus which operates depending on a fact that the tire pressure changes with an amount or rate of change of the rotating speed of the corresponding wheel when an external force acting on the wheel varies for some reason, for example, when the wheel passes a raised portion of the road surface. Since the maximal value of the amount of change of the rotating speed of the wheel decreases with a decrease in the tire pressure, the tire pressure can be estimated on the basis of the detected maximal value of the wheel speed change amount. The tire pressure detecting apparatus in question includes signal generating means for generating a signal when the detected amount of change of the wheel speed is higher than a predetermined threshold value, and tire pressure estimating means responsive to that signal, for estimating the tire pressure on the basis of the maximal value of the wheel speed change amount.
However, the condition of the road surface that permits the above-indicated apparatus to detect the tire pressure is limited. Described in detail, the tire pressure can be estimated from the maximal value of the detected wheel speed change amount, only where the relevant wheel runs over a single projection on the road surface. When the wheel passes successive projections and recesses on a bumpy or washboard road surface, changes of the rotating speed of the wheel due to those projections and recesses overlap each other, whereby the maximum value of the detected wheel speed change amount is not commensurate with the tire pressure, making it impossible to effect accurate detection of the tire pressure.
While the difficulty of detecting the tire pressure of the vehicle wheel has been described above by way of example, it has been difficult to detect the changing states of the other characteristics of the vehicle wheel and/or tire, such as the rotating speed, acceleration and eccentricity of the wheel, replacement of the metal wheel member per se, wear of the tire, and attachment of a foreign matter to the tire.
While it would be easy to estimate the behavior and the changing characteristics of a vehicle wheel if the disturbance or noise which acts on the wheel and influence its behavior and changing characteristics could be accurately detected, there is known no apparatus capable of accurately detecting the disturbance acting on the vehicle wheel.